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Writer's pictureTaliya Mammadhasanzada
Aug 10, 20205 min read

Importance of Process Diagrams in Process Engineering 🧯🗒✏️

Warm greetings to all 🤩 in the 8th post on #Day7! Yes, today I have already completed the 1st week of my challenge journey 👻. Time to continue to learn and share knowledge💡. In this post, we will clarify what are the most useful and needed Process diagrams in Process Engineering, their main advantages, roles and etch. Here we go 🧯,


Introduction 📌

📍Engineering Diagrams are vital for an understanding of a process to chemical

engineers, of equipment to mechanical engineers, of electrical circuits to electrical engineers, and so on. These diagrams are prepared in many different ways to suit the specific requirements. Process Flow Diagrams (PFD) and Piping and Instrumentation Diagrams (P&ID) are basic requirements of process engineering and are prepared before attempting any detailing. Steps followed in the preparation of these diagrams and interpretation of the same are covered in today's post 😉!



Need for PFD and P&ID🛠

💡When any chemical manufacturing project is conceived, immediate information is sought on the requirements of raw materials and utilities. This information can be calculated using the Laws of Conservation of Mass and Energy. When these data are presented in a sequential manner with a symbolic representation of equipment, it is known as Process Flow Diagram (PFD) or Process Flow Sheet. It can be said that PFD is a schematic illustration of the system. It shows relationships between the 📌major components in the system. It also tabulates the process design values for the components.


PIPING & INSTRUMENTATION DIAGRAM (P&ID) is different from PFD🧐

While PFD is a quantitative representation of the process, sequential presentation of flow, piping with instrumentation and controls that are required for the smooth operation of the process are given on a P&I diagram 🧪. It can, therefore, be said that P&ID is a schematic illustration of the functional relationship of piping, instrumentation, and system equipment components. It shows all the piping including the physical sequence of branches, fittings, equipment, instrumentation and control interlocks.


  • PFD is a useful diagram in effective communication of design information.

It helps an operator in adjusting his operating parameters, a shift supervisor in checking the plant operation, management in discussions across the table and project engineers in comparison and evaluation of different processes and their quantitative requirements. Modern plants have extensive instrumentation and controls such that minimum attention is required of an operator. Apart from controlling the plant variables, these plants give better productivity 🧩in terms of yield and quality. Also, less manpower is required to operate the plant with increased safety.



  • Process engineers are involved in the preparation of both these types of diagrams.


Block Diagrams 🖇

📎Simplest flowsheets are block diagrams. Process engineer begins the process design with a block flow diagram in which only the feed and product streams are identified. Such input-output diagrams are not very detailed and as such are most useful in the early stages of process development. This figure 1- *Typical process block diagram for the manufacture of acrylic acid:

The processes, described in the block diagram, are then broken down into basic functional elements such as a reaction and separation sections. 📍Process engineer can also identify

  • the recycle streams and

  • additional unit operations


to achieve the desired operating conditions. Identification of basic elements helps in performing material and energy balance calculations which in turn help in the preparation of the PFD.

Development and Utility of Process Flow Diagrams 🖌

🔎Any product or process development starts with stoichiometric calculations. At first, the required capacity of the final product is fixed. The product can normally be manufactured by inputting different raw materials and following different process routes. For example, the manufacture of ammonia is possible with different hydrocarbon feedstocks such as natural gas, naphtha, fuel oil, coal, etc. Process route for each feedstock is different. For example,

  • reforming is a preferred route for natural gas or naphtha while partial oxidation is the route followed for fuel oil or coal.

  • Nitrogen for the ammonia manufacture is invariably obtained from the air but it may be fed as air or nitrogen is separated from the air by liquefaction and it is fed to the process. PFD (Process Flow Diagram) for each continuous process is different.

  • Another example is the reduction of nitroaromatic compounds to corresponding amines. In a classical Bechamp process, the nitro compound is mixed with water and fine iron powder in a batch reactor.


✂️The reaction mixture is moderately heated in the presence of a catalyst to initiate the reaction (basically in an acidic medium). Hydrogen is generated in situ and reduces the nitro compound to the corresponding amine. The reaction is exothermic and the temperature is controlled by cooling. The reaction takes a long time to complete. The product mixture is separated into organic and aqueous layers. While the aqueous layer is drained out, the organic layer is siphoned and purified by filtration and distillation under vacuum. In the newer version of the process, hydrogen gas is bubbled in the organic liquid under pressure. Nickel or noble metal-based catalyst is used.

 

📌Gas dispersion through the liquid is improved by different methods such as the use of a static mixer, use of gas-induced agitator, liquid jet ejector system, etc. Such a system is quite efficient and the reaction can be completed in a relatively short period. Both the process routes are used in the industry. PFDs for both the routes are different. Above examples involve chemical reactions. However, there are PFDs which involve unit operations but no chemical reactions. For example,

  1. separation of components of natural gas in a distillation column by cryogenic means,

  2. removal of acid gas by absorption–desorption,

  3. removal of Volatile Organic Compounds (VOC) by adsorption–desorption,

do not involve a chemical reaction. Each PFD is, therefore, to be treated on its own requirements.

PFD provides🧐

🔎A Process Flow Diagram generally includes following information:

  1. Flow rate of each stream in case of continuous process or quantity of each reactant in case of a batch process.

  2. Composition of streams

  3. Operating conditions of each stream such as pressure, temperature, concentrations, etc.

  4. Heat added or removed in a particular equipment

  5. Flows and design operating conditions of utilities such as steam, cooling water, brine, hot oil, chilled water, thermic fluid, etc.

  6. Major equipment symbols, names and identification.

  7. Any specific information which is useful in understanding the process. For example, symbolic presentation of a hazard, safety precautions, sequence of flow, etc.






References 📖

  1. Introduction to Process Engineering and Design pg. 80

  2. Winnick, J., Chem. Engg. Prog. 86 (1), 1990, p. 41.

  3. Thodos, G., and L. F. Stutzman, Ind. Engg. Chem., 50 (3), 1958, p. 413.

  4. Prugh, R. W., Chem. Engg. Prog., 70 (11), 1974, p. 72.

  5. Bhatt, B. I., and S. B. Thakore, Stoichiometry, 5th Ed., McGraw Hill Education, New Delhi, 2010.

  6. Guccione, E., Chem. Engg., 72 (4), 1965, p. 144.

  7. Johnson, J. E., and D. J. Morgan, Chem. Engg., 92 (14). 1985, p. 72.


Additional Resources 🧪🔑

You can get deep insight about Process/Chemical Engineering from these sources😉:

  1. https://t.me/chemical_worlds- Chemical Engineering Books, Quizzes and GATE Study Group

  2. https://t.me/chemical_environmental- Discussion group related to Chemical Engineering Problems

  3. https://t.me/chemicalengineeringworld_cew- Everything related to Chemical Engineering

  4. https://t.me/ebookgate- Chemical Engineering E-books (Telegram Channel)

  5. https://www.youtube.com/channel/UCqioh32NOJc8P7cPo3jHrbg- Piping Analysis

  6. https://www.youtube.com/channel/UCQfMyugsjrVUWU0v_ZxQs2Q -Mechanics of engineered devices

  7. http://chemicalengineeringguy.com/- suggests a wide range of courses in Chemical engineering (you can find free courses on topic of Aspen HYSYS, Aspen Plus)

  8. https://www.youtube.com/user/LearnEngineeringTeam- suggests working principles of every engineered devices, equipment and etch.

  9. https://www.youtube.com/channel/UCR0EfsRZIwA5TVDaQbTqwEQ- suggests great information about pumps, compressors with animation.


🔌Today we have already started to learn about Importance of Process Engineering Diagrams, Process Flow Diagrams, their advantages and Block Flow Diagrams.

📌Tomorrow we will continue to learn about details of PFD, PFD examples, P&I Diagrams and development of P&I Diagrams. Now, time to say goodbye👋🏻 until tomorrow and Stay tuned for more content 😉🌝✨!



✏️Note: If you need one of those books or links, you can contact me via my email or LinkedIn profile.

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